Phase modulation device

ABSTRACT

The phase modulation device includes an image data generator, a gradation data generator, an adjustment voltage controller, and a reflective liquid crystal element. The image data generator generates image data corresponding to a distribution of phase change amount or a distribution of phase velocity. The gradation data generator generates gradation data corresponding to each pixel. The reflective liquid crystal element includes a pixel region having a plurality of pixel blocks, and an adjustment electrode. The adjustment voltage controller applies an adjustment voltage having a same voltage value as a driving voltage applied to a pixel electrode of the pixel block adjacent to the adjustment electrode.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation of PCT Application No.PCT/JP2018/037208, filed on Oct. 4, 2018, and claims the priority ofJapanese Patent Application No. 2017-197404, filed on Oct. 11, 2017, theentire contents of both of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a phase modulation device using aliquid crystal element.

In recent years, in an optical communication field, an optical networksystem formed in an annular shape and an optical wavelength divisionmultiplexing communication system have been proposed in order to copewith a rapidly increasing amount of information. A reconfigurableoptical add/drop multiplexer (ROADM) device is used that can performbranching or insertion of an optical signal in these opticalcommunication systems without, relaying conversion to an electricalsignal. In the ROADM device, as an optical switching device, awavelength selective switch (WSS) device is used. As an opticalswitching element in the WSS device, a micro electro mechanical systems(MEMS) mirror, and a reflective liquid crystal element, for example, aliquid crystal on silicon (LCOS) element or the like are used.

The LCOS element is a reflective liquid crystal element having a pixelregion in which a plurality of reflective pixel electrodes are arrangedin a horizontal direction and a vertical direction. A refractive indexof a liquid crystal on each pixel electrode changes by controlling avoltage applied to the liquid crystal for each pixel electrode. Thephase velocity of the signal light is controlled for each pixel bychanging the refractive index of the liquid crystal on each pixel.

The LCOS element can incline a wavefront of the signal light by changingthe phase velocity stepwise for each pixel. The LCOS element can controlan inclination angle of the wavefront of the signal light according to arate of change of the phase velocity. That is, the LCOS elementfunctions as a phase modulation element that reflects the signal lightin a predetermined direction by changing the phase velocity for eachpixel.

The MEMS mirrors are required corresponding to the number of wavelengthbands of the signal light. For that reason, when the wavelength band ofsignal light or the number thereof is changed, the MEMS mirror has to benewly manufactured in accordance with the changed contents.

In contrast, the LCOS element can arbitrarily divide the pixel regioninto a plurality of pixel blocks and can control each pixel block.Therefore, when the wavelength band of signal light or the numberthereof is changed, the pixel block can be reconfigured in accordancewith the changed content, and thus it is not necessary to newlymanufacture a liquid crystal element. That is, the LCOS element issuperior in variable grid property than the MEMS mirror. In JapaneseUnexamined Patent Application Publication No. 2016-143037, an example ofthe phase modulation device using the LCOS element is described.

SUMMARY

Usually, a peripheral region that does not contribute to phasemodulation is formed outside a pixel region adjacent to the pixelregion. Disclination may occur due to a potential difference between thepixel region and the peripheral region. Disclination means that liquidcrystal molecules tilt in a direction different from the intendeddirection due to a potential difference. If the potential difference islarge, the lateral electric field becomes large, so that disclination islikely to occur or the generation area is widened.

Since the signal light is reflected at an inclination angle differentfrom the target inclination angle due to the influence of disclination,the crosstalk incident on an output port different from the targetoutput port occurs.

An aspect of one or more embodiments provides a phase modulation deviceincluding: an image data generator configured to generate image datacorresponding to a distribution of phase change amount or a distributionof phase velocity based on information data; a gradation data generatorconfigured to generate gradation data corresponding to each pixel basedon the image data; an adjustment voltage controller configured togenerate an adjustment voltage based on the gradation data; and areflective liquid crystal element to which the gradation data and theadjustment voltage are applied; wherein the reflective liquid crystalelement includes: a pixel region in which a plurality of pixelelectrodes are arranged, and a driving voltage of a sawtooth waveformvoltage pattern corresponding to the gradation data is applied; and afirst adjustment electrode adjacent to the pixel region in a firstdirection in which the voltage pattern is repeated, the pixel regioncomprises a plurality of pixel blocks configured to modulate the phaseof signal light incident on the pixel region based on the voltagepattern, and to change a wavefront of the signal light, and theadjustment voltage controller applies an adjustment voltage having asame voltage value as a driving voltage applied to a pixel electrode ofa pixel block adjacent to the first adjustment electrode, to the firstadjustment electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a phase modulation deviceaccording to one or more embodiments.

FIG. 2 is a top view illustrating an example of a reflective liquidcrystal element.

FIG. 3 is a cross-sectional view of the reflective liquid crystalelement taken along line A-A in FIG. 2.

FIG. 4 is a cross-sectional view of the reflective liquid crystalelement taken along line B-B in FIG. 2.

FIG. 5 is a diagram illustrating phase modulation of the signal light bya reflective liquid crystal element.

FIG. 6A is a diagram illustrating a driving voltage applied to a pixelelectrode.

FIG. 6B is a diagram illustrating a refractive index of a liquid crystalon the pixel electrode.

FIG. 7 is a diagram illustrating a relationship between a pixel block ina pixel region and an adjustment electrode.

FIG. 8A is a diagram illustrating an example of a voltage pattern of adriving voltage along C1-C2 in FIG. 7.

FIG. 8B is a diagram illustrating an example of a voltage pattern of adriving voltage along D1-D2 in FIG. 7.

DETAILED DESCRIPTION

A phase modulation device according to one or more embodiments will bedescribed with reference to FIG. 1. A phase modulation device 1 includesan image data generator 2, a gradation data generator 3, an adjustmentvoltage controller 5, and a reflective liquid crystal element 10. Thereflective liquid crystal element 10 is an LCOS element, for example.Hereinafter, the reflective liquid crystal element 10 is referred to asan LCOS element 10.

Information data JD is input to the image data generator 2. Theinformation data JD includes a parameter indicating a relationshipbetween positions of an input port and an output port of signal lightand an angle of reflected light with respect to incident light in thesignal light, and a parameter related to a wavelength band of the signallight, that is, a distribution of phase change amount that realizes adesired reflected light angle. The phase change amount is the lead orlag of the phase of the reflected light with respect to the phase of theincident light, and corresponds to the distribution of phase velocity.The signal light emitted from a predetermined input port isphase-modulated by the phase modulation device 1 and enters a targetoutput port.

The image data generator 2 sets the distribution of phase change amountbased on the information data JD. The image data generator 2 generatesimage data DD based on the distribution of phase change amount or thedistribution of phase velocity, and outputs the generated image data DDto the gradation data generator 3. The gradation data generator 3generates gradation data DS corresponding to each pixel in the LCOSelement 10 of the image data DD, and outputs the gradation data DS tothe LCOS element 10 in accordance with the timing of writing to eachpixel. A driving voltage corresponding to this gradation is generated inthe LCOS element 10 and applied to the liquid crystal. The gradationdata generator 3 outputs the gradation data DS to the adjustment voltagecontroller 5.

A configuration example of the LCOS element 10 will be described withreference to FIGS. 2 to 4. The LCOS element 10 includes a drivingsubstrate 20, a transparent substrate 30, liquid crystals 11, and asealing material 12. The driving substrate 20 includes a pixel region21, an alignment film 22, a connection terminal 23, and an adjustmentelectrode 40. In the pixel region 21, a plurality of reflective pixelelectrodes 24 are arranged in the horizontal and vertical directions.One pixel electrode 24 constitutes one pixel.

The alignment film 22 is formed at least on the pixel region 21. Theconnection terminal 23 is formed on the outer peripheral portion of thedriving substrate 20, receives the gradation data DS from the gradationdata generator 3, and receives a timing control signal from the outside.The connection terminal 23 is also connected to a power supply and thelike from the outside.

The adjustment electrode 40 is formed around the pixel region 21 andadjacent to the pixel region 21. The alignment film 22 is formed on thepixel region 21 and the adjustment electrode 40. The connection terminal23 is formed on the outer peripheral portion of the driving substrate 20and connected to the adjustment voltage controller 5 illustrated in FIG.1.

The transparent substrate 30 includes a transparent electrode 31 and analignment film 32. The alignment film 32 is formed on the transparentelectrode 31. The driving substrate 20 and the transparent substrate 30are bonded to each other with a gap by the sealing material 12 so thatthe pixel electrode 24 and the transparent electrode 31 face each other.

The sealing material 12 is formed in an annular shape along the outerperipheral portion of the adjustment electrode 40. In FIGS. 2 to 4, thesealing material 12 is formed in a region outside the adjustmentelectrode 40, but may be formed over a part of the region of theadjustment electrode 40. The liquid crystals 11 are filled in a gapbetween the driving substrate 20 and the transparent substrate 30 andare sealed by the sealing material 12. An anti-reflection film 33 may beformed on the surface opposite to the surface on which the transparentelectrode 31 of the transparent substrate 30 is formed.

A semiconductor substrate (a silicon substrate, for example) can be usedas the driving substrate 20. A drive circuit for driving each pixel isformed on the driving substrate 20. As a material of the pixel electrode24, the connection terminal 23, and the adjustment electrode 40, a metalmaterial containing aluminum as a main component can be used.

As the transparent substrate 30, a non-alkali glass substrate or aquartz glass substrate can be used. As a material of the transparentelectrode 31, Indium Tin Oxide (ITO) can be used. A dielectric film maybe formed above and below the ITO film. As the sealing material 12, anultraviolet curable resin, a thermosetting resin, or a resin that iscured by using both ultraviolet light and heat can be used. As theanti-reflection film 33, a dielectric multilayer film can be used.

The phase modulation of the signal light by the LCOS element 10 will bedescribed with reference to FIGS. 5, 6A, and 6B. In order to make thedescription easy to understand, a case where a pixel block 25 isconfigured by three pixel electrodes 24 will be described. Usually, thepixel block 25 has a configuration in which three or more pixelelectrodes 24 are arranged in the horizontal direction and the verticaldirection, respectively. In order to distinguish each pixel electrode24, it is assumed to be pixel electrodes 24 a, 24 b, and 24 c from theleft.

Based on the image data DD corresponding to the distribution of phasechange amount (distribution of phase velocity) generated by the imagedata generator 2 illustrated in FIG. 1, different driving voltages DVa,DVb, and DVc are applied to the pixel electrodes 24 a, 24 b, and 24 c asillustrated in FIG. 6A. Actually, the driving voltages DVa, DVb, and DVcapplied to the liquid crystals 11 are voltages applied between the pixelelectrodes 24 a, 24 b, and 21 c and the transparent electrode 31. Sincethe liquid crystals 11 have anisotropy in the refractive index and thedielectric constant of the constituent molecules, the refractive indexchanges by changing the tilt of the molecules according to the appliedvoltage.

Therefore, as illustrated in FIG. 6B, the liquid crystals 11 on thepixel electrode 24 a have a first refractive index na, the liquidcrystals 11 on the pixel electrode 24 b have a second refractive indexnb, and the liquid crystals 11 on the pixel electrode 24 c have a thirdrefractive index nc (na>nb>nc). The refractive indexes na to nc areaverage refractive indexes of the liquid crystals 11 on the pixelelectrodes 24 a to 24 c.

Signal light SL output from the input port is incident on the pixelblock 25 in a state of linearly polarized light of p-polarized light ors-polarized light. The alignment films 22 and 32 illustrated in FIG. 3are formed so that the deflection direction of the signal light SL andthe alignment direction of the liquid crystals 11 are the same. Thealignment direction is a direction ire which the liquid crystals 11 inthe vicinity of the alignment film 22 are inclined, for example. Thedirection in which the liquid crystals 11 in the vicinity of thealignment film 32 are inclined may be the alignment direction.

By making be deflection direction of the signal light SL and thealignment direction of the liquid crystal 11 the same, it is possible tosuppress attenuation of the signal light SL caused by the modulation oflinearly polarized light into elliptically polarized light and thep-polarized light having an s-polarized light component or thes-polarized light having a p-polarized light component, and the signallight SL can be efficiently reflected.

Pa, pb, and pc illustrated in FIG. 5 schematically show a difference inthe phase velocity caused by a difference in the refractive index of theliquid crystals 11 on the pixel electrodes 24 a, 24 b, and 24 c. A WFillustrated in FIG. 5 schematically illustrates a wavefront of thesignal light SL. The wavefront WF is a surface in which the phases ofthe signal light SL are aligned. The phase change amount or phasevelocity of the signal light SL increases stepwise from the pixelelectrode 24 a toward the pixel electrode 24 c. As a result, thewavefront WF of the signal light SL can be changed (inclined).

By the driving voltages DVa, DVb, and DVc, an inclination angle θ of thewavefront WF can be increased by increasing the difference in therefractive index of the liquid crystal 11 on the pixel electrodes 24 a,24 b, and 24 c and increasing the difference in phase change. Theinclination angle θ of the wavefront WF can be reduced by reducing thedifference in the refractive index of the liquid crystals 11 on thepixel electrodes 24 a, 24 b, and 24 c, and reducing the difference inthe phase change. The inclination angle θ corresponds to an angle formedby the wavefront WF of the signal light SL and the perpendicular linesof the pixel electrodes 24 a, 24 b, and 24 c. The inclination angle θ ofthe wavefront WF can be changed by changing the number of pixelelectrodes 24.

The signal light SL is reflected by the pixel electrodes 24 a, 24 b, and24 c with the wavefront WF having a predetermined inclination angle θbased on the image data DD generated by the image data generator 2.Therefore, the LCOS element 10 can reflect the signal light SL in apredetermined direction by changing the phase velocity of the signallight SL stepwise for each pixel based on the image data DD.

The LCOS element 10 can control the inclination angle θ of the wavefrontWF of the signal light SL according to the rate of change of the phasevelocity. That is, the LCOS element 10 functions as a phase modulationelement that changes the phase velocity for each pixel and reflects thesignal light SL in a predetermined direction. When the LCOS element 10controls the inclination angle θ of the wavefront WF of the signal lightSL, the signal light SL is incident on a target output port.

The relationship between the pixel block 25 in the pixel region 21 andthe adjustment electrode 40 will be described with reference to FIGS. 7,8A, and 8B. FIG. 7 illustrates a configuration when the pixel region 21illustrated in FIG. 2 is divided into four pixel blocks 25. The signallight SL enters each pixel block 25.

The range and position of the pixel block 25 are determined based on theinformation data JD. The pixel block 25 is configured to include anincident area 26 on which the signal light SL incident. The incidentarea 26 is determined based on the spot diameter, spot shape, incidentposition accuracy, and the like of the signal light SL. The LCOS element10 can reconfigure the pixel block 25 in accordance with the changedcontents of the information data JD.

The LCOS element 10 can control the inclination angle θ of the wavefrontWF of the signal light SL for each pixel block 25 based on the imagedata DD generated by the image data generator 2. In order to distinguisheach pixel block 25, the upper left pixel block 25 is referred to as apixel block 25 a, the lower left pixel block 25 is referred to as apixel block 25 b, the upper right pixel block 25 is referred to as apixel block 25 c, and the lower right pixel block 25 is referred to as apixel block 25 d.

The signal light SL of different wavelength bands can be made incidenton the pixel blocks 25 a to 25 d. The LCOS element 10 can apply drivingvoltages of different voltage patterns to the pixel blocks 25 a to 25 dbased on the image data DD.

A case where a driving voltage DV is controlled by the amplitude of thevoltage value will be described with reference to FIGS. 8A and 8B. FIG.8A illustrates a voltage pattern of the driving voltage DV of thecontinuous pixels along C1-C2 of the pixel block 25 a illustrated inFIG. 7. Although the same voltage pattern as that of the pixel block 25a is illustrated in the pixel block 25 c in FIG. 7, a driving voltage DVhaving a different voltage pattern can be applied.

FIG. 8B illustrates a voltage pattern of the driving voltage DV of thecontinuous pixels along D1-D2 of the pixel block 25 c illustrated inFIG. 7. Although the same voltage pattern as that of the pixel block 25c is illustrated in the pixel block 25 d in FIG. 7, a driving voltage DVhaving a different voltage pattern can be applied.

As illustrated in FIGS. 8A and 8B, the driving voltage DV has a sawtoothwaveform voltage pattern. Since the voltage is actually a voltage foreach continuous pixel, the voltage has a stepped shape, but here, thevoltage is illustrated in a sawtooth shape. In the pixel blocks 25 a to25 d illustrated in FIG. 7, dark portions correspond to low voltageportions of the voltage pattern of the driving voltage DV illustrated inFIG. 8A or 8B, and bright portions correspond to high voltage portions.Since the voltage pattern illustrated in FIG. 8A has a larger amplitudeof the voltage value than the voltage pattern illustrated in FIG. 8B,the inclination angle θ of the wavefront WF of the signal light SLincreases.

Here, it is assumed that the liquid crystals 11 are a horizontallyaligned liquid crystal material, that is, a liquid crystal materialhaving a positive dielectric anisotropy. In a horizontally alignedliquid crystal, the refractive index increases as the voltage amplitudeis increased. In the case of a vertically aligned liquid crystalmaterial, that is, a liquid crystal material having a negativedielectric anisotropy, the refractive index is lowered by increasing thevoltage amplitude. Moreover, the refractive index and the anisotropy ofthe refractive index differ depending on the liquid crystal material. Inaddition, the resulting phase change amount differs depending on thethickness of the liquid crystal layer.

The voltage pattern of the driving voltage DV is set based on the imagedata DD generated by the image data generator 2. Therefore, the rangesand positions of the pixel blocks 25 a to 25 d are determined based onthe information data JD, the incident signal light SL is phase-modulatedbased on the voltage pattern of the driving voltage DV, thereby changing(inclining) the wavefront WF of the signal light SL. The control by aPSM method in which the driving voltage DV is controlled by a pulsewidth or the number of pulses is also effective. In this case, thevertical axis in FIGS. 8A and 8B corresponds to the integration time ofthe applied pulse of the driving voltage DV in one frame.

In order to distinguish each adjustment electrode 40, with respect tothe pixel region 21, the adjustment electrode 40 adjacent to the firstside (upper side in FIG. 7) in a first direction (vertical direction inFIG. 7) in which the sawtooth waveform voltage pattern is repeated isreferred to as an adjustment electrode 41 (first adjustment electrode),and the adjustment electrode 40 adjacent to the second side (lower sidein FIG. 7) opposite to the first side in the first direction is referredto as an adjustment electrode 42 (third adjustment electrode).

With respect to the pixel region 21, the adjustment electrode 40adjacent to the third side (left side in FIG. 7) in the second direction(left-right direction in FIG. 7) orthogonal to the first direction isreferred to as an adjustment electrode 43 (second adjustment electrode),and the adjustment electrode 40 adjacent to the fourth side (right sidein FIG. 7) opposite to the third side in the second direction isreferred to as an adjustment electrode 44 (fourth adjustment electrode).

A blank area 50 that does not contribute to phase modulation may beformed between the pixel blocks 25. FIG. 7 illustrates a case where theblank area 50 is formed between the pixel blocks 25 a and 25 c and thepixel blocks 25 b and 25 d. The blank area 50 may be formed between thepixel blocks 25 a and 25 b and the pixel blocks 25 c and 25 d, or theblank area 50 may be formed on both of them.

The adjustment voltage controller 5 can drive the adjustment electrodes41 to 44 with a voltage signal synchronized with the transparentelectrode 31 based on the gradation data DS.

A case where the driving voltage DV is controlled by the amplitude ofthe voltage value will be described. The adjustment voltage controller 5applies, to the adjustment electrode 41 adjacent to the pixel electrodes24 of the pixel blocks 25 a and 25 c, an adjustment voltage AV havingthe same voltage value as the driving voltage DV applied to the pixelelectrodes 24 of the pixel blocks 25 a and 25 c so that the potentialdifference between the adjustment electrode 41 and the transparentelectrode 31 is the same as the potential difference between the pixelelectrodes 24 of the pixel blocks 25 a and 25 c and the transparentelectrode 31.

The adjustment voltage controller 5 applies, to the adjustment electrode42 adjacent to the pixel electrodes 24 of the pixel blocks 25 b and 25d, an adjustment voltage AV having the same voltage value as the drivingvoltage DV applied to the pixel electrodes 24 of the pixel blocks 25 band 25 d so that the potential difference between the adjustmentelectrode 42 and the transparent electrode 31 is the same as thepotential difference between the pixel electrodes 24 of the pixel blocks25 b and 25 d and the transparent electrode 31.

For example, the voltage value of the driving voltage DV applied to thepixel electrode 24 adjacent to the adjustment electrode 41 in the pixelblocks 25 a and 25 c is assumed to be va, and the voltage value of thedriving voltage UV applied to the pixel electrode 24 adjacent to theadjustment electrode 42 in the pixel blocks 25 b and 25 d is assumed tobe vb (va<vb). The adjustment voltage controller 5 applies an adjustmentvoltage AV having the voltage value va to the adjustment electrode 41,and applies an adjustment voltage AV having the voltage value vb to theadjustment electrode 42.

Therefore, the potential difference between the pixel blocks 25 a and 25c and the adjustment electrode 41 and the potential difference betweenthe pixel blocks 25 b and 25 d and the adjustment electrode 42 can bereduced, so that the occurrence of disclination can be suppressed.

The adjustment voltage controller 5 applies, to the adjustment electrode43 adjacent to the pixel electrodes 24 of the pixel blocks 25 a and 25b, an adjustment voltage AV having an average voltage value or anintermediate voltage value between the maximum voltage value and theminimum voltage value of the driving voltage DV applied to the pixelelectrode 24 adjacent to the adjustment electrode 43. The adjustmentvoltage controller 5 applies, to the adjustment electrode 44 adjacent tothe pixel electrodes 24 of the pixel blocks 25 c and 25 d, an adjustmentvoltage AV having an average voltage value or an intermediate voltagevalue between the maximum voltage value and the minimum voltage value ofthe driving voltage DV applied to the pixel electrode 24 adjacent to theadjustment electrode 44.

Therefore, the maximum potential difference between the pixel blocks 25a and 25 b and the adjustment electrode 43 and the maximum potentialdifference between the pixel blocks 25 c and 25 d and the adjustmentelectrode 44 can be reduced, so that occurrence of disclination can besuppressed.

When the driving voltage UV is controlled by a Pulse Width Modulation(PWM) method, the adjustment voltage controller 5 associates thegradation data in the pixel region 21 with the gradation data in theadjustment electrodes 41 to 44 by the PWM method to generate anadjustment voltage AV and applies the generated adjustment voltage AV tothe adjustment electrodes 41 to 44.

The adjustment voltage controller 5 synchronizes the voltage applied tothe transparent electrode 31 so that the potential difference betweenthe adjustment electrode 41 and the transparent electrode 31 is the sameas the potential difference between the pixel electrodes 24 of the pixelblocks 25 a and 25 c and the transparent electrode 31, in the adjustmentelectrode 41, and applies an adjustment voltage AV having the samevoltage pattern as the driving voltage DV applied to the pixelelectrodes 24 of the pixel blocks 25 a and 25 c adjacent to theadjustment electrode 41.

The adjustment voltage controller 5 synchronizes the voltage applied tothe transparent electrode 31 so that the potential difference betweenthe adjustment electrode 42 and the transparent electrode 31 is the sameas the potential difference between the pixel electrodes 24 of the pixelblocks 25 b and 25 d and the transparent electrode 31, in the adjustmentelectrode 42, and applies an adjustment voltage AV having the samevoltage pattern as the driving voltage DV applied to the pixelelectrodes 24 of the pixel blocks 25 b and 25 d adjacent to theadjustment electrode 42.

The adjustment voltage controller 5 generates an adjustment voltage AVto have an average voltage value or an intermediate voltage valuebetween the maximum voltage value and the minimum voltage value of thedriving voltage DV applied to the pixel electrodes 24 of the pixelblocks 25 a and 25 b adjacent to the adjustment electrode 43, andapplies the generated adjustment voltage AV to the adjustment electrode43 in synchronization with the voltage applied to the transparentelectrode 31.

The adjustment voltage controller 5 generates an adjustment voltage AVto have an average voltage value or an intermediate voltage valuebetween the maximum voltage value and the minimum voltage value of thedriving voltage DV applied to the pixel electrodes 24 of the pixelblocks 25 c and 25 d adjacent to the adjustment electrode 44, andapplies the generated adjustment voltage AV to the adjustment electrode44 in synchronization with the voltage applied to the transparentelectrode 31.

Therefore, the potential difference between the pixel blocks 25 a and 25b and the adjustment electrode 43 and the potential difference betweenthe pixel blocks 25 c and 25 d and the adjustment electrode 44 can bereduced, so that the occurrence of disclination can be suppressed.

In accordance with the phase modulation device 1 according to one ormore embodiments, since the potential difference between the pixelregion 21 and the peripheral region can be reduced by the adjustmentelectrode 40, the occurrence of disclination due to the potentialdifference between the pixel region 21 and the peripheral region can besuppressed.

The present invention is not limited to one or more embodimentsdescribed above, and various modifications may be made thereto withoutdeparting from the scope of the present invention.

What is claimed is:
 1. A phase modulation device comprising: an imagedata generator configured to generate image data corresponding to adistribution of phase change amount or a distribution of phase velocitybased on information data; a gradation data generator configured togenerate gradation data corresponding to each pixel based on the imagedata; an adjustment voltage controller configured to generate anadjustment voltage based on the gradation data; and a reflective liquidcrystal element to which the gradation data and the adjustment voltageare applied; wherein the reflective liquid crystal element comprises: apixel region in which a plurality of pixel electrodes are arranged, anda driving voltage of a sawtooth waveform voltage pattern correspondingto the gradation data is applied; and a first adjustment electrodeadjacent to the pixel region in a first direction in which the voltagepattern is repeated, the pixel region comprises a plurality of pixelblocks configured to modulate the phase of signal light incident on thepixel region based on the voltage pattern, and to change a wavefront ofthe signal light, and the adjustment voltage controller applies anadjustment voltage having a same voltage value as a driving voltageapplied to a pixel electrode of a pixel block adjacent to the firstadjustment electrode, to the first adjustment electrode.
 2. The phasemodulation device according to claim 1, wherein the reflective liquidcrystal element further comprises a second adjustment electrode adjacentto the pixel region in a second direction orthogonal to the firstdirection, and the adjustment voltage controller applies an adjustmentvoltage of an average voltage value of a driving voltage applied to apixel electrode of a pixel block adjacent to the second adjustmentelectrode, to the second adjustment electrode.
 3. The phase modulationdevice according to claim 1, wherein the reflective liquid crystalelement further comprises a second adjustment electrode adjacent to thepixel region in a second direction orthogonal to the first direction,and the adjustment voltage controller applies an adjustment voltage ofan intermediate voltage value between a maximum voltage value and aminimum voltage value of a driving voltage applied to a pixel electrodeof a pixel block adjacent to the second adjustment electrode, to thesecond adjustment electrode.
 4. The phase modulation device according toclaim 1, wherein the information data includes a parameter indicating arelationship between positions of an input port and an output port ofthe signal light and an angle of reflected light with respect toincident light in the signal light, and a parameter of a wavelength bandof the signal light.